1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to an air cooled turbine stator vane with micro cooling channels.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
Pressurized cooling air used to cool both rotor blades and stator vanes is bled off from the compressor and is thus not available for producing useful work such as burning with a fuel to produce a hot gas stream that is passed through the turbine. The more bleed off air used from the compressor for cooling of the airfoils, the lower the efficiency of the engine.
Prior art turbine stator vanes and rotor blades are formed by casting the vanes or blades with the internal cooling air circuit formed during the casting process. Some machining can be used after the casting process such as to form the film cooling holes. An investment casting process uses a ceramic core having the shape of the desired internal cooling circuit. Molten metal is poured around the ceramic core and solidified to form the vane or blade. Because the core is made of a ceramic material, the size of the cooling features is limited to around 1.3 mm in diameter for a cooling air hole. Smaller features would break during the casting process because of the heavy molten metal flowing around the small ceramic features. Also, because of a pulling direction for casting the ceramic mold, complex features in the cooling circuitry cannot be produced. Smaller and more complex cooling air features would allow for improved cooling effectiveness while using less cooling air from the compressor.